associated with organic acids, bitterness is often the result of phenolic compounds, saltiness is attributable to sodium or potassium, and sweetness is the result of sugars, including fructose, glucose, and sucrose ( Sims and Golaszewski, 2003 ). Sugars not
Kyle M. VandenLangenberg, Paul C. Bethke, and James Nienhuis
Antal Szőke, Erzsébet Kiss, László Heszky, Ildikó Kerepesi, and Ottó Toldi
In all eukaryotic cells, fructose 2,6-bisphosphate (fru 2,6P 2 ) is an important regulator of carbohydrate metabolism ( Okar and Lange, 1999 ). In plants, this molecule coordinates the rate of CO 2 assimilation and carbon partitioning between
Rui Zhou* and Lailiang Cheng
Cytosolic fructose-1,6-bisphosphatase (cytoFBPase) (EC 22.214.171.124) occupies a strategic site in sucrose synthesis and has been demonstrated to play a key role in carbon partitioning between sucrose and starch in non-sorbitol forming plants. In addition to sucrose and starch, Sorbitol is the primary photosynthetic end product in the leaves of many tree fruit species in the Rosaceae family. To understand the biochemical regulation of photosynthetic carbon partitioning between sorbitol, sucrose and starch in sorbitol synthesizing species, we purified cytoFB-Pase to apparent homogeneity from apple leaves. The enzyme was a homotetramer with a subunit mass of 37 kDa. It was highly specific for fructose-1,6-bisphosphate with a Km of 3.1 μm and a Vmax of 48 units/mg protein. Either Mg2+ or Mn2+ was required for its activity with a Km of 0.59 mm and 62 μM, respectively. Li+, Ca2+, Zn2+, Cu2+ and Hg2+ inhibited whereas Mn2+ enhanced the Mg2+-activated enzyme activity. Fructose-6-phosphate was found to be a mixed type inhibitor with a Ki of 0.47 mm. Fructose 2,6-bisphosphate (F2,6BP) competitively inhibited the enzyme activity and changed the substrate saturation curve from hyperbolic to sigmoidal. Adenosine monophosphate (AMP) was a non-competitive inhibitor for the enzyme. F2,6BP interacted with AMP to inhibit the enzyme in a synergistic way. Dihydroxyacetone phosphate did not have inhibitory effect on apple leaf cytosolic FBPase activity. Sorbitol increased the susceptibility of the enzyme to the inhibition by F1,6BP. The presence of sorbitol in the reaction mixture led to a reduction in the enzyme activity.
Hisashi Kato-Noguchi and Alley E. Watada
This study was undertaken to determine the effect of low-O2 atmosphere on the concentration of fructose 2,6-bisphosphate (Fru-2,6-P2), which can activate the enzyme pyrophosphate-dependent:phosphofructokinase (PPi-PFK) to catalyze the reaction from fructose 6-phosphate to fructose 1,6-bisphosphate (Fru-1,6-P2). Fru-2,6-P2 remained unchanged in carrot (Daucus carota L.) root shreds stored under air, but it increased 3.0- and 5.3-fold at 2% and 0.5% O2 atmosphere, respectively, at 5C, and the increases were almost twice as great at 15C. The concentration of PPi ranged from 17 to 33 nmol·g-1 fresh weight, which is more than sufficient for the PPi-PFK to proceed. Thus, low-O2 atmosphere appeared to hasten glycolysis of carrot shreds by increasing Fru-2,6-P2, which activated PPi-PFK toward glycolysis.
Dingbo Zhou and Theophanes Solomos
The mechanism of C2H4 action on plant respiration is not well understood. In the present work we treated peeled sweet potato roots (Ipomea batatas cv. MD715) with 10 ppm C2H4 in air and 3% O2 Analytical data showed a close relationship between respiration and activity of phosphofructokinase while the activity of pyrophosphate fructose-6-phosphate phosphotransferase remained constant under all experimental treatments. At the respiratory peak there was an increase in both pyruvate and fructose-2,6-diphosphate. The change in the levels of pyruvate, followed closely that of the respiration drift, while those of fructose-2,6-diphosphate did not correlated so closely. The data indicate that the stimulation of respiration by C2H4 in sweet potato roots is closely associated with an enhancement of glycolysis. The levels of ATP also increased with the rise in respiration and reflected the magnitude of the respiratory increment.
Wesley Gartner, Paul C. Bethke, Theodore J. Kisha, and James Nienhuis
showed that 80% of the soluble carbohydrate that accumulated in cotyledons was sucrose, with less than 5% each of glucose and fructose ( Patrick and McDonald, 1980 ). Significant accumulation of seed dry weight begins ≈8–12 d after fertilization, stops
Ya-Ching Chuang and Yao-Chien Alex Chang
·L −1 sucrose, 20 g·L −1 fructose, or 20 g·L −1 glucose, alone or plus 200 mg·L −1 8-HQS; and distilled water as a control ( Table 1 ). These concentrations were chosen according to previous literature ( Ichimura and Korenaga, 1998 ; Islam et al
Mark J. Howieson and Nick Edward Christians
a polymer of fructose with a terminal glucose moiety ( Chatterton et al., 1989 ). Increased catabolism and decreases in levels of fructans have been observed in grasses in response to defoliation ( Morvan-Betrand et al., 2001 ; Prud'homme et al
Thomas E. Marler and Nirmala Dongol
group of plants. A plant’s NSC pool is composed of low molecular weight sugars (the most abundant free sugars in plants are the disaccharides sucrose and maltose, and the monosaccharides glucose and fructose) plus starch ( Chapin et al., 1990 ). A
Marija Perić, Slavica Dmitrović, Suzana Živković, Biljana Filipović, Marijana Skorić, Ana Simonović, and Slađana Todorović
well as for tissue cultures of some woody plants, including Corylus avelana ( Yu and Reed, 1993 ), Quercus suber ( Romano et al., 1995 ), and Prunus mume ( Harada and Murai, 1996 ). Compared with sucrose, glucose and fructose are better carbon